Yark, like 'fuck' can be used as any part of speech. The true definition of Yark will not be revealed, as only a select four know the actual definition.

As an verb: I'm gonna yark when I get home.
Can you please yark me now.
As an adjective: Your extreme degree of yark makes me hot.
As a noun: My favorite toy is yark.
As an adverb: My sllab is so itchy that its beyond the yarky mark.